DL/I

DL/I, Data Language/I, is how programs work with IMS databases. IMS stores data in a hierarchy, like a tree: a customer at the top, the customer's accounts below, each account's transactions below that. DL/I calls move around that tree.

The calls have short names. GU, get unique, goes directly to a record that matches a condition. GN, get next, reads the next record in order. GNP, get next within parent, reads only the records under the current parent, such as the transactions of one account. Adding an H, as in GHU, holds the record so it can be changed. REPL replaces it, DLET deletes it, and ISRT inserts a new one.

A COBOL program makes a call through the CBLTDLI interface, passing the function code, a PCB that names the database view, an area for the data, and optional segment search arguments, SSAs, which say what to look for.

After every call, the program checks the status code in the PCB. Blank means success, GE means not found, and GB means the end of the database was reached. It is the IMS equivalent of checking SQLCODE.